Reporting a new ciliate, <i>Hemiurosomoida linea</i> n.sp. from a freshwater pond of Rajghat, Delhi, India

Hemiurosomoida was established as a new genus by Singh and Kamra in 2015 based on its morphology, morphogenesis and molecular analysis. Based on their morphology, the members of this genus were earlier erroneously placed in the genus Oxytricha, then shifted to another genus Urosomoida, before establishing the new genus Hemiurosomoida. However, a detailed molecular analysis based on small subunit ribosomal RNA (SSU rRNA) showed that the members of this genus are rather placed far apart from the other two genera in the phylogenetic tree. Therefore, they are now placed in a new genus Hemiurosomoida. To date, four species of this genus have been reported, viz. H. longa, H. warreni, H. tibetensis and H. koreana. In the present investigation, a new freshwater species, Hemiurosomoida linea n. sp. was reported from a freshwater pond located in Rajghat, Delhi, India. Diagnostic features of H. linea include- a flexible body with an average size of 81x18 µm (protargol stained cells); narrowly elongated cells with a rounded anterior end and a tapering posterior end; the presence of 2 macronuclear nodules and 2 micronuclei; the presence of only 17 Frontal-Ventral-Transverse (F1-8, V1-5, T1-4) cirri, the transverse cirri (T1-4) being arranged in a linear row; four dorsal rows of bristles (DK1-3 and DM1); 2 caudal cirri; an average of 19 adoral membranelles; 17 right marginal and 17 left marginal cirri; no fragmentation of DP3; a flat and narrow buccal cavity, and undulating membranes (UMs) in typical Oxytricha pattern. Thus, this study has unravelled and confirmed that H. linea was a new species and helped expand the knowledge base of ciliate biodiversity in India.